Dispersion processes for polymerizing fluoro olefin monomers in aqueous media are well known. Such processes employ a surfactant to provide stability to the aqueous dispersion of particles of resulting fluoropolymer. Different surfactants are chosen for use in dispersion polymerization because of their influence on reaction rate, dispersed fluoropolymer particle size, dispersion stability, color and the like.
Kappler and Lina disclose a process for the manufacture of fluoropolymer by polymerization of an aqueous dispersion of vinylidene fluoride in WO2005/121290, said dispersion containing a fluorosurfactant chosen from one or more of the following products: Rf(CH2CF2)m-1—(CH2)nCO2M [1] Rf(CH2CF2)mSO2M [2] Rf(CH2CF2)m(CH2)nSO2M [3], wherein Rf is a linear or branched perfluoroalkyl group comprising form 1 to 5 carbon atoms, m is an integer from 2 to 6, n is an integer from 0 to 2, and M is a hydrogen atom or an alkali metal atom or an ammonium group or an ammonium group comprising at least one lower alkyl substituent.
Polymerization of other monomers, such as tetrafluoroethylene with hexafluoropropylene or perfluoro(methyl vinyl ether) are very sensitive to chain transfer during the polymerization. The vinylidene fluoride, as taught by WO 2005/121290 is less sensitive to such chain transfer. It is desirable to have a polymerization process that can be employed with these more sensitive monomers using a surfactant containing low levels of fluorine.
It is also known that the presence of a fluorocarbon “tail” in the hydrophobic segment of surfactants provides extremely low surface energy. Such fluorinated surfactants are much more surface active than their hydrocarbon counterparts. For surfactants having fluorochemical chains, longer perfluoroalkyl chains contain a higher percentage of fluorine at a given concentration and typically provide better performance. However, the fluorinated materials derived from longer perfluoroalkyl chains are more expensive. Therefore, it is desirable to reduce the fluorine content with delivery of the same or higher performance.
The present invention provides a polymerization process using a surfactant containing low levels of fluorine which is effective with monomers sensitive to chain transfer.